n = int(input())
s = input()
pos = [[0]*3 for i in range(3)]
for i,c in enumerate(s):
  if c == "c":
    pos[0][i%3] += 1
  elif c == "o":
    pos[1][i%3] += 1
  elif c == "n":
    pos[2][i%3] += 1

now = 0
ans = 0
for i in range(3):
  cc,oo,nn = pos[0][(0+i)%3], pos[1][(1+i)%3], pos[2][(2+i)%3]
  mn = min(cc,oo,nn)
  ans += mn

print(ans)